JPS5840512Y2 - current limiting fuse - Google Patents

Description

[Detailed explanation of the invention] This invention makes the slope of the long-time region of the current hourly characteristic gentler, quickly cutting off all the fault current that would blow out the fuse element, and also making it possible to provide overload protection. This relates to current limiting fuses.

In conventional high-voltage current-limiting fuses of this type, for example, the protection cooperation between the transformer and the fuse was not sufficiently satisfactory when the fuse alone was used.

That is, in the protective coordination characteristics of the transformer and current-limiting fuse shown in Figure 5, A is the transformer's magnetizing inrush current, B is the overload deterioration area of the transformer, and C and D are the I of the conventional high-voltage current-limiting fuse.
- is the characteristic, and E is the characteristic I- of an overload protection device inserted in series with a conventional current limiting fuse.

As is clear from these, when using the conventional current limiting fuse alone, it is not possible to obtain a characteristic I- that exhibits only a characteristic that does not invade the areas A and B, so overload protection is provided with the help of characteristic E. It was customary to do so.

Therefore, by using a highly reliable high-voltage, current-limiting fuse that has a gentle long-term slope of the I- characteristic of the fuse itself, and can quickly cut off all the current that is characteristic of I-, it is possible to improve the quality of electrical equipment. There has been a strong demand for protection.

In general, high-voltage fuses that cut off fault current when it flows through a circuit are broadly classified into current-limiting fuses and expulsion fuses.

In the former case, when the fault current is large, the fuse element fires instantaneously and uniformly over the entire length of the fuse element, providing sufficient dielectric recovery power and being able to quickly shut off the fault current. If the current is relatively small, several times the rated current, the element will only partially fuse and arc, making it impossible to obtain sufficient dielectric recovery strength, and as a result of the arc continuing for a long time, thermal damage is destroyed and becomes uninterruptable.

As described above, it has the disadvantage that it is difficult to cut off fault currents in a small current range rather than large currents.

In addition, in the latter case, the decomposition gas of the arc extinguisher and metal vapor generated when the arc is generated are discharged outside the bay if necessary to extinguish the arc. A fault current can be easily cut off, but a large current range will greatly increase the pressure generated within the fuse cylinder, eventually destroying the fuse cylinder and making it impossible to shut off.

For this reason, in the case of an expulsion fuse, contrary to the above-mentioned current limiting fuse, a small current has better breaking performance.

Therefore, it has been extremely difficult to create a compact high-voltage fuse that can safely and reliably cut off fault currents from small current ranges to large current ranges.

This idea was made with these points in mind, and it provides a high-voltage current-limiting fuse, a so-called wide-area fuse, that can safely and reliably cut off all currents with fusing characteristics from small current ranges to large current ranges. be.

An embodiment of this invention will be described below based on the drawings.

In Fig. 1, 1 is a fuse cylinder made of an insulator;
A support 2 made of an inorganic material and this support 2
It has a plurality of fuse elements 3 made of silver spirally wound according to the rated current around the outer periphery of the fuse element 3, and the periphery thereof is filled with an arc extinguishing agent 4 such as silica sand.

The ends of the fuse element 3 are attached by screws 7 to end spacers 5, 6 attached to both ends of the support 2.

Reference numeral 8 denotes a kip that closes both ends of the cylindrical body 1. 9 is fuse
It is a covering body that surrounds a predetermined part of the element 3 with a gap, and this part is constructed as shown in FIG.

That is, the center part of the fuse element 3 is coated with a low-temperature melting metal 10 such as tellurium, and when an overcurrent flows through the element and the temperature reaches 351°C, eutecticization of silver and tellurium progresses, and the low temperature melts. It is fused by becoming a molten alloy.

The low-temperature melting metal 10 can also be obtained by other methods such as gold-silicon alloy, but silver-tellurium coated metal is much cheaper.

Both ends of the envelope 9 are plugged with a heat insulating material 11 to prevent the arc extinguishing agent 4 from entering.

12 is an air layer between the envelope 9 and the fuse element 3.

This invention enables the following two points with the above-mentioned configuration.

First of all, the low-temperature melting of the fuse element due to the low-temperature metal 10 in the tellurium-coated portion and the air layer 12 in the envelope slits greatly reduce heat transfer from the fuse element in the simple radial direction. Therefore, the fusing always occurs in this part.

Then, the gradient of the I- characteristic in the long-time region becomes gentle.

That is, Fig. 3a shows a case where a conventional Ag wire element is filled with an arc extinguishing agent 4 such as silica sand, and Fig. 3a shows a case where tellurium is applied to the center of the silver wire element in the state shown in a. , Figure C shows the average fusing characteristics when a silver wire coated with tellurium is inserted as a fuse element in the part surrounded by the envelope as shown in Figure 2.

As an example, if the two-hour fusing current is expressed as ■2h, ■2h', and ■2h'' in each case of Fig. 3 a, l), and c,
I2h'/■2h''=0,67I2h''/■2h=F-
The result is 0.67, and the effect is remarkable.

Moreover, the fault current in a small current range can be cut off by the envelope.

This is the same as the breaking operation of an expulsion fuse, and the internal pressure increases due to the decomposition gas generated from the inner wall of the envelope that occurs when an arc occurs, and the pressure gradient created when it blows out from both ports of the envelope 9. and the flow velocity cool the arc.

This situation is shown in a and b in FIG.

That is, Fig. 1a shows the decomposition gas generated from the inner wall of the envelope at the time of arc ignition with the arrow 13, and Fig. 3 shows the situation just before the ignition is interrupted, and the high-temperature decomposition gas released to the outside of the envelope is shown. Gas A
g Steam blows out violently, but the arc extinguisher around the envelope 9 rapidly absorbs heat, forming a hemispherical falgelite (
The molten silica sand) 14 is formed to complete the cutting.

Therefore, the satisfactory characteristic of curve F shown in FIG. 5 is obtained.

As a result, the envelope will not be thermally deformed up to around 351°C, the melting point of the fuse element, and when an arc occurs, a large amount of gas (flammable gas) will be generated and the internal pressure will rise. A material with sufficient mechanical and thermal strength is selected.

As a specific example, a second insulating member such as alkali-free glass cloth, which has a high heat resistance and high insulation resistance at high temperatures, is impregnated or coated with a first insulating member such as silicone rubber. .

Regarding the dimensions of the envelope, the length is 50 to 80 mm, and the inner diameter is 1
~3 mm is appropriate.

As described above, this invention has an extremely simple structure that can safely and reliably cut off all of the fault current that would cause the fuse element to melt, whereas conventionally the limit for breaking the current was several times the rated current. can also be
The overload protection performance and range can also be improved by making the slope of the I- characteristics gentler in the long-term region.
This makes it possible to obtain an extremely excellent high-voltage fuse.

[Brief explanation of drawings]

Fig. 1 is a side sectional view showing a current limiting fuse that is an implementation of this invention, Fig. 2 is a partial configuration diagram showing an enlarged view of the main parts of this invention, and Fig. 3 shows the average fusing characteristics of the current limiting fuse. Figure 4 is an explanatory diagram showing the operating state of the main parts of this invention,
FIG. 5 is a diagram showing the protection cooperation characteristics of the transformer and current limiting fuse. In the figure, 1 is a cylinder, 3 is a fuse element, 4 is an arc extinguisher, 9 is an envelope, and 10 is a low-temperature melting metal. Note that the same reference numerals in the figures indicate the same parts.

Claims (1)

[Scope of utility model registration request] A fuse element supported in an insulating cylinder and provided with a low temperature melting part in a predetermined portion, and an envelope surrounding the low temperature melting part with a gap in between, the fuse element having the above-mentioned a first insulating member that has heat resistance near the melting point of the low-temperature melting part and generates flame-retardant gas by an arc during melting; and a first insulating member that has better mechanical strength and heat resistance than the first insulating member. and a second insulating member impregnated or coated with the first insulating member.